This invention relates to an ignition coil apparatus for an internal combustion engine having a plurality of spark plugs.
FIG. 7 illustrates a conventional ignition coil apparatus, from which it is seen that four spark plugs #1 to #4 are arranged in a straight line on a rocker cover 2 of a cylinder head of an internal combustion engine. A first ignition coil 3, which is the simultaneous ignition type, is connected through high-tension electrical conductors 5 to the first and the fourth plugs #1 and #4, and a second ignition coil 4, which is the simultaneous ignition type, is connected through high-tension electrical conductors 5 to the second the the third plugs #2 and #3.
High voltage generated in the ignition coils 3 and 4 are applied to the first to the fourth plugs #1 and #4 through the electrical conductors 5.
In the conventional ignition coil apparatus for an internal combustion engine, the relatively long high-tension electrical conductors 5 must extend from the remotely located ignition coils 3 and 4 to the respective plugs #1 to #4 on the engine. Therefore, the generated voltage and the generated energy are decreased due to the resistance and the capacitance of the high-tension electrical conductors 5. Also, since the number of the electrical conductors 5 extending externally of the engine 1 is equal to the number of the spark plugs #1 to #4, the design lay out in the engine compartment is accordingly limited, and the assembly of the installation of the engine is not easy.
Further, as illustrated in FIGS. 8 and 9, the rocker cover 2 of the engine cylinder head has a plurality of ring-shaped ridges or circular seal ribs 6 each formed around plug openings 7 in the rocker cover 2 for receiving the spark plugs therein. Each of the circular seal ribs 6 are engaged by plug caps (not shown) placed over the high-tension electrical conductors 5 in order to establish a water-proof and electrically insulating seal between the conductors 5 and the rocker cover 2.
However, since the waterproof arrangement by the individual plugs caps is provided for each of cylinders or eahc of the spark plugs or the high-tension electrical conductors, the overall structure is complicated and water can stay on the rocker cover to destroy electrical insulation.